(a) Field of the Invention
The present invention relates to transmission technology, and more particularly to a speed-reduction transmission bearing, which steadily supports the transmission mechanism and achieves high reduction ratio transmission.
(b) Description of the Prior Art
An axle bearing is used to support a motor shaft in axial direction as well as radial direction, maintaining the motor shaft in a centralized position during rotation, enhancing the slidability of the motor shaft and reducing its friction. However, a regular axle bearing does not provide other functions. To enable an axle bearing to be used in a speed reduction transmission mechanism, for example, for a motor to rotate a transmission shaft in a speed-reduction manner, the aforesaid conventional axle bearing cannot achieve a speed reduction function. In this case, a speed-change mechanism (for example, speed-change gearbox) has to be used and coupled between the motor and the transmission shaft for reducing the speed of the rotary power of the motor shaft of the motor by means of multiple gears and then transferring the speed-changed rotary power to the transmission shaft. The installation of the speed-change mechanism greatly increases the size, making the system impractical for use in a precision machine (such as robotic arm) or any other tools with a small installation space.
Further, harmonic drives have been used in industrial motion control, machine tool, robotics and many other fields for gear reduction. Exemplars are seen in U.S. Pat. Nos. 4,625,582, 5,662,008, 7,552,664, 4,909,098, EP0514829, etc. A harmonic drive apparatus includes a circular spline having a number of internal teeth, a radially flexible cylindrical flexspline having outer spline teeth engageable with the internal teeth of the circular spline, and a wave generator disposed within the flexspline in engagement with the flexspline. The circular spline, the flexspline, and the wave generator are rotatable around a rotational axis. The number of the external spline teeth of the flexspline is smaller than the number of the internal spline teeth of the circular spline. The wave generator has a cam section which generates a circumferential wave of radial deflection of the flexspline for causing the external spline teeth thereof to locally engage with the internal spline teeth of the circular spline. The cam section has elasticity in its radial direction sufficient for biasing the flexspline against the circular spline to absorb any play between the flexspline and the circular spline. According to this prior art design, the fabrication of the radially flexible cylindrical flexspline is complicated. Further, radial deflection of the flexspline cannot assure fully engagement between the external spline teeth and the internal spline teeth. Further, the harmonic drive apparatus has a large length in the axial direction, limiting its application to precision machines.
Further, US Pub. 20130081587 discloses a harmonic gear drive, which includes a circular spline and a dynamic spline, a flexspline disposed within the circular spline and the dynamic spline, a wave generator assembly disposed within the flexspline, and a rotational actuator connectable to the wave generator. The wave generator assembly includes an elliptical wave generator surrounded tightly with an inner race having an inner race axial end, an outer race surrounded tightly with the flexspline, a plurality of balls disposed between the inner race and the outer race, and a ball cage having an annular section disposed axial from the balls proximal to the inner race axial end and a plurality of ball separators extending axially from the annular section such that consecutive balls are separated by one of the ball separators. According to this design, the circular spline and the dynamic spline are arranged in a parallel manner and can be forced to move apart in axial direction. To prevent relative displacement between the circular spline and the dynamic spline, a housing is needed to house the circular spline and the dynamic spline. However, the use of the housing greatly increases the dimension of the system and its manufacturing cost.
Therefore, how to combine a speed-reduction mechanism and an axle bearing into a compact and simple speed-reduction transmission bearing for use in a precision machine (such as robotic arm) to provide support and to achieve speed-reduction transmission is the focus of the technical features of the present invention.